The invention generally relates to a technique and apparatus to measure a fuel cell parameter.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:H2→2H++2e− at the anode of the cell, and  Equation 1O2+4H++4e−→2H2O at the cathode of the cell.  Equation 2
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to form the anode and cathodes of each fuel cell. In this manner, reactant gases from each side of the PEM may leave the flow channels and diffuse through the GDLs to reach the PEM.
The fuel cell stack typically is part of a fuel cell system that includes the fuel cell stack; power conditioning circuitry to convert power from the fuel cell stack into the proper form for an AC load; an air blower to furnish an oxidant reactant stream to the fuel cell stack; a fuel processor to furnish a fuel reactant stream to the fuel cell stack; and many other components to control and aid the operation of the fuel cell stack. The fuel cell system typically includes a large number of sensors for purposes of diagnosing conditions in the fuel cell system and controlling the fuel cell system accordingly. For example, these sensors may measure voltages, currents, a humidification level, a carbon monoxide level, etc., for purposes of detecting potential problems with the fuel cell stack, such as problems that are attributable to corrosion, stack assembly (as examples), and for purposes of regulating operation of the stack, such as regulating reactant flow rates to set stoichiometric ratios and regulating the cooling of the stack, (as examples). A potential challenge with the use of many different sensors is that the sensors themselves may complicate the design of the fuel cell system and may significantly contribute to the overall cost of the fuel cell system.
Thus, there is a continuing need for better ways to diagnosis and control a fuel cell system.